How does DKIM signing work step-by-step?

This is what happens when you send a signed message:

• Your mail system selects a DKIM selector.
• It loads the private key.
• It hashes the message body.
• It hashes specific headers.
• It combines those elements to create a cryptographic signature.
• It adds the DKIM Signature header to the email.
• The recipient later verifies that signature using the public key in DNS.
• All of this happens behind the scenes during the voyage.